Document: WG14 N1670

Possible defect report: G.5.1: -yv and -x/v are ambiguous

Submitter: Fred J. Tydeman (USA)
Submission Date: 2013-01-07
Subject:Possible defect report:G.5.1: -yv and -x/v are ambiguous

The tables in G.5.1 have the mathematical formulas -yv and -x/v. I believe that they are ambiguous as they could have two meanings:

• (-y)/v and (-x)/v
• -(y/v) and -(x/v)

I believe it matters for at least these cases:

1. The two operands are different NaNs, negate flips the sign of a NaN, and the result of * and / depends upon the sign and value of the NaN.
2. The result is a NaN from non-NaN operands, negate does not flip the sign of a NaN, while both * and / set the sign of the result as the XOR of the signs of the operands.
3. All operands are non-NaN, the result is inexact and non-NaN, and a rounding that is not symmetric about zero is in effect.